The task of this master's thesis was to describe FACTS devices and their application in the transmission network. The first chapter presents a general overview of FACTS technology and describes the flow of power through the power line. The next chapter describes the types of FACTS devices and their division into series, parallel and combined devices. Typical arrangements are shown for each type of device, and their working principle is described. The most common versions of parallel compensation devices are SVC and STATCOM, and the most common series compensation devices are TCSC and SSSC. A combined series-series device is an IPFC, and a combined series-parallel device UPFC. The installation of a series compensation device was shown on a model of transmission network in Istria. The simulation was performed in the DIgSILENT PowerFactory program, and two possible connections of TCSC device to the power grid were analyzed. Their influence on the increase in the power transfer capacity of the transmission line is shown, and the optimal installation location of the device was selected.